1. Field of the Invention
The present invention relates to an inkjet head and a manufacturing method thereof, and more specifically to an inkjet head for discharging ink by using a piezoelectric element, and a manufacturing method of the inkjet head wherein wiring for discrete electrodes is formed by the aerosol method.
2. Description of the Related Art
Conventionally, an inkjet recording apparatus (an inkjet printer) that has an inkjet head (ink discharge head) with a plurality of arranged nozzles (ink discharge ports) and form images on a recording medium by discharging ink (ink droplets) from nozzles toward the recording medium as the inkjet head moves relative to the recording medium, are known as an image forming apparatus.
For example, a known ink discharging method in such an inkjet recording apparatus is a piezoelectric method in which a diaphragm constituting a portion of a pressure chamber (ink chamber) is deformed by the deformation of a piezoelectric element (piezo element) so as to change the volume of the pressure chamber. Therefore, ink is introduced from an ink supply channel to the pressure chamber when the volume of the pressure chamber increases, and the ink in the pressure chamber is discharged as droplets from the nozzle when the volume of the pressure chamber decreases.
In inkjet recording apparatuses as well, it is desirable to record images that have the same high quality as transfer prints, and to achieve this end, the size of the nozzle must be made smaller to reduce the size of the ink droplet discharged from the nozzle, and the nozzles must be more densely arranged.
Thus, in order to increase the density of the nozzles (recording dots), one known example is to reduce breakages in the electrode wiring portion by setting the width of the wiring portion in at least one of the electrodes which are disposed on both the pressure chamber side of the piezoelectric element and on the side opposite to the pressure chamber, so as to be smaller than half the maximum width of the aperture of the hollow portion of the pressure chamber (referred to Japanese Patent Application Publication No. 2001-80068). Therefore, it is possible to reduce the size of the inkjet head, and to increase the density of the dots by manipulating the wiring portion of the electrodes.
Similarly, another known example is to set the width of the wiring portion so as to be less than ⅓ the maximum width of the aperture of the hollow portion of the pressure chamber (referred to Japanese Patent Application Publication No. 2003-154646, for example).
In those above examples of prior art, an insulating layer is interposed on the common electrode side to inactivate the bottom portion of the wiring.
Also, for example, an aspect is known as each piezoelectric actuators in which surface side electrodes and the signal line or conductive layer corresponding to the flexible wiring substrate are electrically connected via a single solder bump so as to have that has the desired gap (referred to Japanese Patent Application Publication No. 2003-69103). Therefore, it is enable to be high-density electrical joining between the wiring substrate and the flat piezoelectric actuator elements disposed in a high-density array (i.e., a matrix array).
Conventionally, in order to achieve a higher nozzle density in the inkjet heads in this manner, a method for keeping the wiring to ½ (or ⅓) or less the width of the pressure chamber aperture, or provide a flexible connection using a solder bump correlated with the matrix array is known as one of the methods for providing wiring from the piezoelectric element to the flexible printed circuit board (FPC) or another external electrode lead portion. Also, for except the field of inkjet head, the aerosol method as described below is known as the method to form the circuit substrate, the wiring of the capacitors or display, and the like.
As used herein, the term “aerosol method” refers to aerosol gas deposition or simply gas deposition, the powder method, or the like. These methods are to blow argon or another carrier gas onto ultrafine PZT particles (lead zirconate titanate Pb(Zr, Ti)O3), the fine PZT particles taken up by the gas are discharged together with the gas through a spray nozzle at high speed to the substrate to deposit the particles, and the substrate is heated to form a film. Therefore, since the above described aerosol methods directly deposit particles to form a film, it is possible to obtain a wide range of film thicknesses.
For example, a known method which forms a very small, ultrafine particle film with good accuracy to the desired area alone entails covering the substrate with a mask and blowing ultrafine particles onto the circuit substrate by way of an aperture to form an ultrafine particle film (referred to Japanese Patent Application Publication No. 06-093418). Therefore, it is possible to form a very fine pattern with a high aspect ratio without bleeding.
Also, according to a circuit substrate which is integrally formed resistors, capacitors, and other passive elements, processes are known in which at least a portion of the resistors, capacitors, and other passive elements are formed by an ultrafine particles film that is formed with the gas deposition method. In particular, while the deposit position of the ultrafine particles is determined by the nozzle position, dielectric components and electrodes are formed by gas deposition (referred to Japanese Patent Application Publication No. 05-048235). Therefore, since the product is devoid of thermal degradation, it is possible to expand the degree of freedom for substrate materials and formation materials.
Furthermore, there are known methods for fabricating conductive members in which, for example, wiring on a substrate and wiring for simple matrix organic EL display apparatuses are connected by using the inkjet method or the gas deposition method (refer to Japanese Patent Application Publication No. 2003-152299, for example). Therefore, it is possible to connect conductive members without an insulating layer.
However, according to configurations with high-density wiring from the piezoelectric elements to the flexible printed wiring board and the circuit board as cited in Japanese Patent Application Publication Nos. 2001-80068 and 2003-154646, it is possible to configure with up to four rows by arranging two rows in a configuration as shown in FIG. 6 of Japanese Patent Application Publication No. 2001-80068, for example. But, when the matrix array has six or eight rows, there is drawback in which the width of the wiring must be made as narrow as possible due to the nozzle pitch so that the wiring resistance increases.
Also, in conventional methods such as sputtering and vapor deposition, since a thickness of several μm or more is difficult from the aspect of the film formation rate, the width of the wiring cannot be significantly reduced. In those conventional methods, it is also necessary to use a mask in locations in which film is not desired because the film is applied to the entire surface. Therefore, there are drawbacks in which removal and surface polishing must be carried out in later steps in order to make the electrodes independent.
It is possible to form electrodes with a high aspect ratio where plating is concerned. However, while masking is required, the current density and the hardness of plating film vary depending on the shape of the wiring pattern. Therefore, there is a drawback in which it is difficult to form a wiring pattern with a constant hardness.
In view of the above, it is possible to consider a method in which a solder bump is used as described in Japanese Patent Application Publication No. 2003-69103. However, soldering in a two-dimensional array is also technically difficult from aspects of surface accuracy, warping, or pressure conditions. In addition, there are also drawbacks such as degradation of element characteristics and the flow of solder into active areas due to soldering in the vicinity of active areas.
Furthermore, the methods as described in Japanese Patent Application Publication Nos. 6-93418, 5-48235, and 2003-152299, are not related to above described inkjet recording apparatuses. Therefore, those cannot directly be used for forming wiring in inkjet heads.